Kokkos static CRS graph row view is too tightly typed

[maartenarnst]

During siam cse, we discussed with @brian-kelley about using static crs graph with a custom type as the data type.

issue 1

This led us to look at such a use, which led us to the following line in the static crs graph row view helper structure:

kokkos/containers/src/Kokkos_StaticCrsGraph.hpp

Line 149 in 32868fa

using ordinal_type = const typename GraphType::data_type;

It is used afterwards in the ‘colidx’ getter both as the ordinal type for the index and as the value type for the return value. This seems appropriate if the data type is an integral type. But, in a use case in which it’s for instance a floating type or a custom type, it seems too restrictive. It seems it prevents static crs graph to be used with non integral data type.

Similarly, in the static crs graph class itself, there seem to be similar issues, where the data type is also used as the ordinal type.

Issue 2

We also wonder why the row view structure is used. Since the stride is always 1, it seems that a kokkos subview could be used instead too.

kokkos/containers/src/Kokkos_StaticCrsGraph.hpp

Line 392 in 5ad6096

return GraphRowViewConst<StaticCrsGraph>(entries, 1, count, start);

[brian-kelley]

Thanks for writing this @maartenarnst .

I guess the main questions for Kokkos core are:

• is it appropriate to let StaticCrsGraph be a more general 2D ragged array type, instead of being only for storing a graph as a sparse adjacency matrix, and
• if not, should there be a separate type for 2D ragged arrays, using offsets+data?

It seems to me that relaxing the assumption that data_type is an integer (option 1) doesn't seem very difficult.

[crtrott]

I think we can consider this.